1. Field of the Invention
This invention relates to a phenol-aldehyde resin which is particularly suited as a bonding agent for the manufacture of wood materials, such as fiberboard and chipboard. More particularly, this invention relates to phenol-aldehyde resins prepared from phenol, formaldelyde and isobutryaldehyde.
2. Prior Art
For the manufacture of wood materials, such as fiberboard and chipboard, alkaline-condensed phenol-formaldehyde resins are preferred as bonding agents, because they release only little formaldehyde, unlike urea and melamine resins, and because they impart to the finished panels very good mechanical properties, especially good water and weathering resistance. Hence phenol-formaldehyde resins are preferred as bonding agents for the manufacture of post-formable hardboard used in the building, automobile, furniture and interior decoration industries.
Wood materials, e.g. fiberboard, are manufactured by impregnating the fibers or chips with the aqueous bonding agent solution and adding mineral acid or aluminum sulfate until a pH-value of approx. 3.0 to 4.5 is attained, so that the resin precipitates and deposits on the fibers. The thus-glued fibers are then pressed at elevated temperatures to produce panels of the required size and thickness.
The resins employed as bonding agents in the preparation of wood fiber products must be such that the formed panels exhibit a satisfactory flexural strength after pressing and conditioning and prior to post-curing and the loss in flexural strength of the panels after immersion in water (for three minutes at 90.degree. C.) must not be excessive.